#include <stdio.h>

// 一键切换大小写输出
// #define CAPITAL_LETTER

int main()
{
    char str[] = "Hello World";
    char c;
    int i = 0;

    while ((c = str[i++]) != '\0')
    {
#ifdef CAPITAL_LETTER
        if (c >= 'a' && c <= 'z')
        {
            c = c - 0x20;
        }
#else
        if (c >= 'A' && c <= 'Z')
        {
            c = c + 0x20;
        }
#endif
        printf("%c", c);
    }
    printf("\n");

    return 0;
}